Challenge

It is easy to boost power with turbine inlet cooling in hot, dry climates. Watson Cogen needed a system that would increase power and efficiency in a cool, humid environment.

Solution

Watson Cogen installed four MeeFog turbine inlet cooling systems to supplement the cooling provided by its existing evaporative coolers. Later it found that it could get better performance under typical operating conditions by removing the evaps and going strictly with fogging.

Watson Cogeneration Venture

Carson, California USA

With four 84.5 MW GE Frame 7EA turbines, each with a duct fired HRSG, and two Dresser Rand steam turbine generator sets, the Watson Cogeneration Plant in Carson, California is one of the largest cogen facilities in the western United States. The plant’s primary function is to provide high pressure steam to the neighboring 275,000 barrel per day BP refinery. The electricity generated is split between the co-owners BP and Edison Mission Energy.

“As the BP refinery grows, it requires more steam for the processes,” says principal engineer Steve Ingistov. “We have two steam turbine generators, but the refinery is taking so much of the steam we are generating, that sometimes we shut down one steamer.”

To maximize output, whether or not the steam turbines are operating, Ingistov uses MeeFog inlet cooling on all turbines, even when the air is cool and humid.

Evaps Aren’t Enough

Watson Cogen has gone through several stages in optimizing the power output from its turbines. Initially it installed 240 gpm evaporative coolers; however, at that flow rate, the inlet air was carrying water droplets past the inlet air filter. Those droplets were striking the compressor blades, so Ingistov had to reduce the flow rate to 150 gpm. To make up for the cooling lost by this lower flow rate, in 1998 Watson Cogen installed a Mee fogging system on each turbine to supplement the evaporative coolers.

“An evaporative cooler is a crude device in comparison to a fogging system,” says Ingistov. “Evaps are simple and reliable, but especially when the air is cool and there is high relative humidity, evaporative cooling is doing next to nothing but fogging is still efficient.”

Instead of going with the standard Mee package, Watson Cogen ordered a custom system which included advanced instrumentation, a pressure vessel and a submicron filter for the water. Initially the nozzles were installed upstream of the silencers, but he found that the fog washed off the dirt that had collected on the silencers and carried it into the compressor where it fouled the blades, so they were subsequently moved downstream of the silencers.

Ingistov aggressively manages his fogging system to get the greatest output from his generators. The turbines operate 8000 hours per year, and he uses fog whenever the temperatures are above 50° F, producing an extra 2.5 MW per turbine.

Reducing Water Usage

As Ingistov continues to research ways to improve his inlet cooling, the latest step is to completely eliminate the evaporative coolers.

“There is a lot we have learned since 1998,” he says. “We first went through a learning curve, then an evolutionary phase. Now we are in a revolutionary phase in getting rid of the evaporative coolers.”

The plant relies on recycled water for cooling and the amount of water available for this function may be curtailed in the future. The evap coolers have a once-through design, so only a small portion of the water actually evaporates with the rest passing down the drain. With the fogging units, on the other hand, all the water goes into cooling the air. The foggers also eliminate the drop in air velocity produced by the evaporative coolers, allowing more air to flow into the turbines.

“It might just be a fraction of an inch, but it is still there, and if the media is dirty the Delta-P (pressure) goes up” says Ingistov.

So, while it seemed like a good idea to eliminate the evaps, Ingistov still wanted hard data to prove that the foggers alone could provide the same cooling and power boost that the evaps and foggers provided working in tandem.

Real World Results

While there are ways to model and calculate efficiency, nothing compares with real world measurements. Since Watson Cogen had four identical machines running continuously on site, it could conduct its own controlled experiment. In October 2010, Watson Cogen removed the evaporative cooler and existing fogging array from Unit 4, replaced them with 600 new fogging nozzles (20 fog lines with 30 nozzles each), and then compared the performance over the following months. The efficiency and output of the units varied during the day and over the months depending on the ambient conditions. On an unusually hot April day when the temperature approached 90 degrees, Unit 4 started out as the leader in the morning, but as the day progressed, the units with the evaps surpassed it. However, there are few such days in Carson. The August afternoon highs only average in the upper 70s, with the humidity high year round from the nearby Pacific.

“Today the weather is the opposite, and Unit 4 without the evap is doing the best,” says Ingistov. “What this means is that when it is relatively cool and the relative humidity is high, the evap cooler does next to nothing while fog does very well.”

Based on these results, he is removing the rest of the evaps and going with fogging only.

About Mee Industries Inc.

Mee Industries Inc. is the innovative, high technology corporation that provides highly customized, cost-effective fog solutions for a wide range of applications including gas turbine inlet air cooling. Founded in 1969 by former Cornell University Research Scientist, Thomas Mee Jr., today the company also specializes in revolutionary fog solutions for industrial humidification, outdoor air conditioning, greenhouse climate control, wine barrel humidification and unique special effects applications.

Renowned MeeFog™ turnkey solutions include meticulously designed and engineered, premium quality, integrated systems that deliver an unequaled combination of price and performance. Mee Industries products are backed by our experienced staff of technical personnel including leading researchers, project managers and engineers along with production and installation specialists. An active research and development division ensures our position of technological leadership in the fog system market. Mee Industries is a proud ISO 9001 certified corporation and manufactures components to meet exacting UL or CE requirements.

Mee Industries is a privately held company with corporate headquarters in Irwindale, Calfornia.